As trends in the tire industry continue toward the use of layered or multicomponent extrudates, the methods for adjusting the extruders used to manufacture multicomponent extrudates is becoming increasingly important. Multiple cold pin feed extruders are typically used to manufacture such extrudates. Since each of the extruders operates at its own screw speed, each extruder must be individually adjusted to contribute the desired amount of each material to the one-piece multicomponent extrudate or composite profile.
Variations in material temperature and material properties render adjustment of the extruders to predetermined screw speeds based on temperature set points an inadequate means of correction. Where the extruders are inadequately adjusted, expensive extrudate material must often be discarded if the extrudate is over or under the specified dimensions of the profile. Additionally, operators must spend valuable time repeating manufacture of the extrudate to obtain a composite profile having the desired dimensions.
One example of a method used to make extruder adjustments is provided in U.K. Patent No. 2,141,844 (which corresponds to U.S. Pat. No. 4,515,738). Pneumatic or ultrasonic spacing measurement devices are used to measure the spacing between the extruded composite profile and the devices. The measured space between the devices and the extrudate is then compared with the desired and expected space. In the event the measured space differs from the desired value, the speed of one of the extruders is adjusted until the measured and desired values are equal.
In another patent, U.K. Patent No. 2,166,568, the operating pressures and temperatures of the individual extruders used to produce the composite extrudate are measured. Upon exiting the extruder, the extrudate is weighed to obtain its actual weight per unit length. The measured weight is then compared with the desired weight per unit length of an extrudate which has the specified dimensions. In the event the actual weight differs from the desired weight, the measured pressures and temperatures are compared to the desired pressure and temperature values for the extruders. Where the measured pressures and temperatures differ from their desired values, they are adjusted, such that the actual weight per unit length of the composite extrudate is adjusted to the desired value.
Unfortunately, such pressure and temperature adjustment methods are not believed to be reliable, since the pressure and temperature measurements relied upon also include changes due to variations in material properties.